On Replication July 2006 Yin Chen

What is? Why need? Types? Investigation of existing technologies –IBM SQL replication –Sybase replication –Oracle replication –MySQL replication –Globus DRS –EGEE RMS –SRB Our project –Goals –Solutions –Features Overview

Copying of data & synchronization of updating Is not Cashing –Client phenomenon –Only for improving response time Is not a Backup (not automatically overwritten when the original data is modified ) Is not a replicated system –deal with when/where to copy –Optimization (how much replica needed …) –Grow or shrink replication tree What is replication?

Data consolidation (central audit & analyse) Data distribution (for branch offices) Performance –Access efficiency (moving data near apps.) –Load balance (distributing access load) –Security (data protection) –Availability (off-line access) –Reliability (disaster recovery, avoiding single point of failure) Data Grid (to improve availability, response time, fault tolerance) Digital Library (copying digital doc, index … ) Why we need it?

Synchronous Replication: What is: updating two storages at the same time; roll back if one fails Benefits: High availability/auto fail-over/minimal data loss Usages: Disaster recover Drawbacks: Network efficiency /scalability/cost/less flexibility Asynchronous Replication: What is : changes are captured on the primary storage and immediately / timely propagated Benefits: low cost / scalability /flexibility Usages: load balance/off-line access/access efficiency Drawbacks: data lost / network bandwidth Replication types

Existing technologies IBM Replication  WebSphere Information Integrator V8.2  Supports multivendors DB  Admin: create replication criteria  control table  Capture: use log/trigger to capture the changes  temp table  Apply: scheduled apply transactions accumulated  target DB  Alert Monitor: monitor and notify users  Supports: after-image copy / before-image copy (can rollback)  Allows subset/simple view/ complex joins & unions copy  Asynchronous replication, allows specifying schedule IBM Replication

Sybase Replication  Pioneer, Since 1993  “publish-and-subscribe” approach  Replication Agent: runs on each publisher, detects changes base on logs  Replication Server: apply changes to target DBs (use pre-configured intelligent routes)  Replication Server Manager: GUI-based, manage/monitor P2P env.  Stable Queues: temporary storage of data, ensure no data is lost  Is advanced in providing high performance Sybase Replication

Oracle Replications Multimaster ReplicationMaterialized View Replication  Multimaster Replication  P2P structure  Changes are pushed to every other site (synchronous/ asynchronous)  Conflicts may happen (Update conflict/Uniqueness conflict /Delete conflict )  Materialized View Replication  One master site manages several non-master sites (keep one/partial copy)  Updatable  Refresh (fast refresh/ complete refresh/ force refresh)  Hybrid Replication Oracle Replications

MySQL Replications 1. simple master/slaver 3. dual masters 2. one slave two masters 4. dual master with slaves 5. master ring 6. master ring with slaves MySQL Replications  Basic replication services, using a light weight Master-Slave model  The master writes updates to logs; the slave reads and executes the queries from the master’s logs  the slave checks results on both sites, replication stops if query only succeeds on one site  This simple structure can be combined arbitrarily to build complex architectures  In a slow network, it is difficult for a slave to catch up with the master – improved in 4.0 by adding relay logs  Have to lock or restart the master for initial snapshot copy

Existing technologies Globus DRS  A client creates a request file (requested file name & target location) and sends to DRS  The Replicator checks user’s credential, and query RLI to find the LRC that contain mappings for the requested file  Also queries each remote LRC to get the physical file names, and selects a best one  Then starts RFT to transfer files.  Finally, registers the new replica to its LRC. The LRC will updates LRI to make replica visible

Existing technologies EGEE RMS  Designed for large, read-only, file replicating among heterogeneous resources  Implement File Catalogues  Replica Location Service maps replica’s Grid Unique ID to physical location  Local Replica Catalogues provides information of replicas for a single VO  Replica Metadata Catalogue maps file’s logical name to Grid Unique ID  LCG File Catalogue is used for performance issues EGEE RMS

Existing technologies Application DISPATCHER: monitors input port and dispatches requests to handler High Level Request Handler MCAT Remote SRB Low Level Request Handler File system drivers Unitree HPSS UNIX DBMS drivers DB2 Oracle ObjectStore Illustra SRB  Enables file searching by attributes  MCAT a database system storing metadata  one or more Master daemon processes having SRB Agent running on them  The dispatcher monitors incoming requests and pass to HLRH (can retrieve metadata from local/remote MCAT) or LLRH (can retrieve data from storage)  supports synch/asynch replication, MCAT replication

Combining DB2 SQL Replication with OGSA- DAI technologies Grid-enabling DB2 Replication to provide a grid service interface for managing replication. Supporting more scalable, secure, high performance data access Extend OGSA-DAI to provide more powerful capabilities. Explore metadata technologies Our Goals

System architecture Metadata Catalogue Relational Database Replication Mechanism Replication Control Service GridFTP Transfer Data Resource Data Replica

Workflows Request Replication Control Service Metadata Search Engine Metadata Register Initiator Selector Starter Metadata Catalogue Relational Database Replication Mechanism GridFTP Transfer Data Resource Replication Target

Features Keeping the features of relational database replication Adding Grid’s features Using Grid service discovery mechanism Supporting more replication scenarios

Introduction of replication Introduction of existing technologies –Relational database replications are advanced in flexibility, offering solutions for frequent updating, update everywhere, data conflictions… –Grid file replications are good at scalable, secure, and efficient file transferring We studied both model and combine the two structures to gain benefits from both Summary